This invention relates generally to the field of seals to prevent loss of vaporized liquids from a container. More particularly, the invention relates to the field of seals utilized to prevent vapor loss from large storage tanks. Even more particularly, the invention relates to the field of seals used to prevent vapor loss in large storage tanks having slotted gauge poles for measuring and sampling the stored liquid.
Many liquids, including volatile liquids such as gasoline or oil, are stored in large bulk storage tanks or containers. These storage tanks are sized to hold millions of gallons of liquid. It is very important, from both an economical and an environmental perspective, to minimize the loss of liquid through vaporization. Obviously, the simplest solution was to provide the tanks with a cover or roof. A fixed roof, however, allowed for the build-up of vapors within the tank as the level of liquid was lowered, leading to a dangerous situation when the liquids stored were flammable or explosive in vapor form. This led to the development of tanks having floating roofs which move vertically in relation to the height of the liquid in the tank, thereby eliminating the air gap between liquid surface and roof. Such structures still require access means to measure or sample the liquid, the access means being relatively small diameter wells positioned in the roof through which fixed gauge poles extend vertically. The gauge poles are slotted along their length to allow the liquid to enter their interior, where a sample could be drawn by lowering a small device into the gauge pole from on top of the roof. The wells, however, allow for air to liquid contact, which allows vaporization and loss of liquid. A sliding well cover, with a small aperture surrounding the gauge pole, is used to seal off the well, but there is still a significant amount of vapor loss, even if a floating seal is positioned in the interior of the slotted gauge pole. For example, in a tank with a capacity of 2,600,000 gallons of gasoline, there is an average loss of about 8,000 gallons of gasoline per year by vaporization escape to the atmosphere through a gauge pole with a floating internal seal and the sliding cover.
It is an object of this invention to provide an apparatus which prevents loss of vaporized liquid through the gauge pole and sliding cover. It is a further object to provide such an apparatus which does not interfere with the workings of either the gauge pole, sliding cover or floating roof. It is a further object to provide such an apparatus which can be installed easily in existing tank structures.